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The bvr locus of Listeria monocytogenes mediates virulence gene repression by beta-glucosides.

ABSTRACT: The beta-glucoside cellobiose has been reported to specifically repress the PrfA-dependent virulence genes hly and plcA in Listeria monocytogenes NCTC 7973. This led to the hypothesis that beta-glucosides, sugars of plant origin, may act as signal molecules, preventing the expression of virulence genes if L. monocytogenes is living in its natural habitat (soil). In three other laboratory strains (EGD, L028, and 10403S), however, the effect of cellobiose was not unique, and all fermentable carbohydrates repressed hly. This suggested that the downregulation of virulence genes by beta-glucosides is not a specific phenomenon but, rather, an aspect of a global regulatory mechanism of catabolite repression (CR). We assessed the effect of carbohydrates on virulence gene expression in a panel of wild-type isolates of L. monocytogenes by using the PrfA-dependent phospholipase C gene plcB as a reporter. Utilization of any fermentable sugar caused plcB repression in wild-type L. monocytogenes. However, an EGD variant was identified in which, as in NCTC 7973, plcB was only repressed by beta-glucosides. Thus, the regulation of L. monocytogenes virulence genes by sugars appears to be mediated by two separate mechanisms, one presumably involving a CR pathway and another specifically responding to beta-glucosides. We have identified in L. monocytogenes a 4-kb operon, bvrABC, encoding an antiterminator of the BglG family (bvrA), a beta-glucoside-specific enzyme II permease component of the phosphoenolpyruvate-sugar phosphotransferase system (bvrB), and a putative ADP-ribosylglycohydrolase (bvrC). Low-stringency Southern blots showed that this locus is absent from other Listeria spp. Transcription of bvrB was induced by cellobiose and salicin but not by arbutin. Disruption of the bvr operon by replacing part of bvrAB with an interposon abolished the repression by cellobiose and salicin but not that by arbutin. Our data indicate that the bvr locus encodes a beta-glucoside-specific sensor that mediates virulence gene repression upon detection of cellobiose and salicin. Bvr is the first sensory system found in L. monocytogenes that is involved in environmental regulation of virulence genes.

SUBMITTER: Brehm K

PROVIDER: S-EPMC93992 | biostudies-literature | 1999 Aug

REPOSITORIES: biostudies-literature

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The bvr locus of Listeria monocytogenes mediates virulence gene repression by beta-glucosides.

Brehm K K Ripio M T MT Kreft J J Vázquez-Boland J A JA

Journal of bacteriology 19990801 16

The beta-glucoside cellobiose has been reported to specifically repress the PrfA-dependent virulence genes hly and plcA in Listeria monocytogenes NCTC 7973. This led to the hypothesis that beta-glucosides, sugars of plant origin, may act as signal molecules, preventing the expression of virulence genes if L. monocytogenes is living in its natural habitat (soil). In three other laboratory strains (EGD, L028, and 10403S), however, the effect of cellobiose was not unique, and all fermentable carboh ...[more]

PMID: 10438775

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Project description:BackgroundListeria monocytogenes, an intracellular foodborne pathogen, infects immunocompromised hosts. The primary route of transmission is through contaminated food. In the gastrointestinal tract, it traverses the epithelial barrier through intracellular or paracellular routes. Strategies to prevent L. monocytogenes entry can potentially minimize infection in high-risk populations. Listeria adhesion protein (LAP) aids L. monocytogenes in crossing epithelial barriers via the paracellular route. The use of recombinant probiotic bacteria expressing LAP would aid targeted clearance of Listeria from the gut and protect high-risk populations from infection.Methodology/principal findingsThe objective was to investigate the ability of probiotic bacteria or LAP-expressing recombinant probiotic Lactobacillus paracasei (Lbp(LAP)) to prevent L. monocytogenes adhesion, invasion, and transwell-based transepithelial translocation in a Caco-2 cell culture model. Several wild type probiotic bacteria showed strong adhesion to Caco-2 cells but none effectively prevented L. monocytogenes infection. Pre-exposure to Lbp(LAP) for 1, 4, 15, or 24 h significantly (P<0.05) reduced adhesion, invasion, and transepithelial translocation of L. monocytogenes in Caco-2 cells, whereas pre-exposure to parental Lb. paracasei had no significant effect. Similarly, Lbp(LAP) pre-exposure reduced L. monocytogenes translocation by as much as 46% after 24 h. Lbp(LAP) also prevented L. monocytogenes-mediated cell damage and compromise of tight junction integrity. Furthermore, Lbp(LAP) cells reduced L. monocytogenes-mediated cell cytotoxicity by 99.8% after 1 h and 79% after 24 h.Conclusions/significanceWild type probiotic bacteria were unable to prevent L. monocytogenes infection in vitro. In contrast, Lbp(LAP) blocked adhesion, invasion, and translocation of L. monocytogenes by interacting with host cell receptor Hsp60, thereby protecting cells from infection. These data show promise for the use of recombinant probiotics in preventing L. monocytogenes infection in high-risk populations.

Project description:While the stress-responsive alternative sigma factor sigma(B) has been identified in different species of Bacillus, Listeria, and Staphylococcus, the sigma(B) regulon has been extensively characterized only in B. subtilis. We combined biocomputing and microarray-based strategies to identify sigma(B)-dependent genes in the facultative intracellular pathogen Listeria monocytogenes. Hidden Markov model (HMM)-based searches identified 170 candidate sigma(B)-dependent promoter sequences in the strain EGD-e genome sequence. These data were used to develop a specialized, 208-gene microarray, which included 166 genes downstream of HMM-predicted sigma(B)-dependent promoters as well as selected virulence and stress response genes. RNA for the microarray experiments was isolated from both wild-type and Delta sigB null mutant L. monocytogenes cells grown to stationary phase or exposed to osmotic stress (0.5 M KCl). Microarray analyses identified a total of 55 genes with statistically significant sigma(B)-dependent expression under the conditions used in these experiments, with at least 1.5-fold-higher expression in the wild type over the sigB mutant under either stress condition (51 genes showed at least 2.0-fold-higher expression in the wild type). Of the 55 genes exhibiting sigma(B)-dependent expression, 54 were preceded by a sequence resembling the sigma(B) promoter consensus sequence. Rapid amplification of cDNA ends-PCR was used to confirm the sigma(B)-dependent nature of a subset of eight selected promoter regions. Notably, the sigma(B)-dependent L. monocytogenes genes identified through this HMM/microarray strategy included both stress response genes (e.g., gadB, ctc, and the glutathione reductase gene lmo1433) and virulence genes (e.g., inlA, inlB, and bsh). Our data demonstrate that, in addition to regulating expression of genes important for survival under environmental stress conditions, sigma(B) also contributes to regulation of virulence gene expression in L. monocytogenes. These findings strongly suggest that sigma(B) contributes to L. monocytogenes gene expression during infection.

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The bvr locus of Listeria monocytogenes mediates virulence gene repression by beta-glucosides.

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The bvr locus of Listeria monocytogenes mediates virulence gene repression by beta-glucosides.

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